This invention relates to a method for producing carbon fiber chopped strands.
Main uses of PAN (polyacrylonitrile) carbon fibers and pitch carbon fibers are space vehicle materials, sliding members, cement reinforcing materials, etc. If it becomes possible to reduce cost by improvement of techniques for production of carbon fibers, it can be expected that these fibers can be further used in automobile field.
It should be noted that except for use in space vehicle field, mostly, these fibers are produced by cutting and chopping long carbon fibers or tow carbons fibers to a specific length (for example, 1-25 mm).
However, with reference to PAN carbon fibers, they are on the market in the form of well bundled short and thin chopped strands, but with reference to pitch carbon fibers, they have not yet been made in the form of chopped strands having properties satisfactory for molding operation and for uniform dispersion and good in orientation and bundling of fibers.
This invention relates to a method for easy production of carbon fiber chopped strands excellent in molding operability and low in transport cost due to high bulk density.
Hitherto, chopped strands have been produced from pitch carbon fibers by infusing and carbonizing pitch fibers spun in the form of short cotton by centrifugal spinning method or turbulence spinning method, then making them into tow by carding and thereafter cutting the tow to a suitable length.
However, chopped strands made by such methods are not only ununiform in fiber length, but are difficult to form into a dense structure with fibers being arranged in a specific direction and satisfactorily oriented, and a cotton-like structure of high bulkiness is formed.
Therefore, even if a binder is applied to the above-mentioned tow and thereafter the tow is cut, it becomes totally or partially cotton-like and it is impossible to obtain chopped strands of 0.2 g/cm.sup.3 or higher in bulk density.
Owing to this high bulkiness, there have been problems such as high transport cost, and severe troubles in production of molding materials such as inferior operability in blending with resins and molding.